Download free "Introduction to Nuclear and Particle Physics.pdf The goal of elementary particle physics is to ¯nd and understand the funda- mental laws of nature which govern how matter interacts. We call an interaction anything that changes the state of matter. We believe that this matter, this means the world around us, is constructed from a few building blocks called elementary particles. If we know precisely how the microscopic world is constructed, then, at least in principle, we know how macroscopic and chemical processes behave. Everything can in principle be explained as an interaction of elementary particles.

Today we know that the world around is constructed from a few atoms. Using some basic laws of quantum mechanics it is actually possible to get an approximate value for the size of the hydrogen atom. If we try to describe the atom using the laws of classical physics, we would ¯nd that the atom is unstable since the electron is performing an accelerated motion in the electrical ¯eld generated by the proton. As a consequence the electron would emit its energy in the form of radiation. The atom would be unstable with a lifetime of less than 10¡9s. But quantum mechanically the situation is completely di®erent. Indeed, an atom is only stable if it is described with the laws of quantum mechanics.